[ID] => 9879
[post_author] => 34
[post_date] => 2018-07-25 09:24:53
[post_date_gmt] => 2018-07-25 08:24:53
[post_content] => It is remarkable that, after decades of warnings, HCB’s monthly Incident Log regularly carries reports of accidents – often including fatalities – during plant start-up after maintenance shutdowns and turnarounds.
Indeed, the Center for Chemical Process Safety (CCPS), an industry-sponsored membership organisation that identifies and addresses process safety issues in the chemical, pharmaceutical and petroleum industries, has determined that most process safety incidents occur during plant start-up, even though that represents only a tiny portion of the operating life of plant. CCPS data indicates that incidents during start-up are five times more likely than during normal operations.
The US Chemical Safety Board (CSB) has now published a Safety Digest to remind operators of the particular risks during start-up operations. To prevent such incidents, CSB says, operators should employ effective communication, provide employees with relevant and appropriate training, and have in place up-to-date and effective procedures to deal with start-up and shut-down activities.
CSB’s Safety Digest highlights three incidents that offer insights into how such incidents occur and can provide lessons to help minimise the risk of future events.
In March 2001, three workers were killed at the BP Amoco plant in Augusta, Georgia. Workers were opening the cover on a polymer catch tank when the cover unexpectedly blew off, expelling hot polymer that killed the three men; it also released a vapour cloud that subsequently ignited.
CSB’s investigation into the incident revealed that an attempt to re-start the plant 12 hours earlier had failed due to mechanical problems downstream of the reactor. However, the partial start-up had delivered an unusually large volume of partly reacted material to the catch tank, which then over-pressurised.
In October 2002, three workers were injured by an explosion at the First Chemical Corp plant in Pascagoula, Mississippi. Steam leaking through manual valves heated mononitrotoluene (MNT) in a chemical distillation column; the column had been shut down five weeks prior to the incident and was thought to be isolated and in standby mode. The hot MNT decomposed, forming unstable chemicals and leading to a runaway reaction.
CSB’s investigation found that the facility lacked an effective system for evaluating hazards and for sharing safety information between the various operating teams.
In August 2008, two people were killed at the Bayer CropScience plant in Institute, West Virginia when a runaway chemical reaction in a residue treater caused a vessel in the methomyl unit to explode. The unit had been out of service while the original residue treater was replaced and a new control system installed.
CBS’s investigation determined that the pre-start-up safety review and turnover practices had not be applied to the redesign process. Further, new equipment had not been calibrated or tested before the restart and employees had not been adequately trained to operate the new unit and control system.
ELEVEN PILLARS OF WISDOM
Considering these and other similar events, CSB has identified eleven key principles that should be followed to ensure that effective process safety management avoids incidents like this.
- Written operating procedures for start-up must be based on a thorough safety review, follow proper safe work practices for opening lines and equipment, and incorporate a management of change (MOC) analysis if any new equipment, process or procedure is not a replacement in kind.
- Written operating procedures need to be sufficiently detailed to avoid the potential for valve misalignment during start-up or shut-down; checklists and diagrams to verify proper valve positioning should be provided.
- Frequently, operational variances were adopted ahead of start-up when the impact of the variance was unknown. A review of MOC policy should be undertaken to address such variances. For this policy to be effective, it is vital to understand the safe limits for process conditions and variables and to understand established operating procedures. Effective training needs to be provided so that employees can recognise when those limits are being exceeded.
- A facility’s lockout/tagout system must require that equipment is rendered safe prior to inspection or maintenance. Operating procedures should include a stop-work provision in the event that safe operating conditions cannot be verified.
- Proper procedures must be in place – and be followed – to isolate equipment after shut-down. A single block valve closure cannot be relied on; a double block and bleed, blind flange or physical disconnection can ensure proper isolation. Equipment placed in standby mode must be monitored while offline; operating procedures must identify the conditions under which standby equipment must be shut down.
- Computerised control systems should include a process overview and, if appropriate, material balance summaries to ensure full process oversight by operators.
- In complex and critical process systems, multi-channel communication with feedback provides the best opportunity for operators to establish and maintain a common understanding of the process unit and its expected future state. During abnormal operating conditions, such as unit start-up, this becomes crucial. Effective communication and feedback is essential.
- Operators must be supervised and supported by experienced and technically trained employees during start-up and shut-down. They must also be fully trained on the control systems they use. It is worth considering the use of simulators to help train personnel to deal with abnormal situations.
- Shift rotation should recognise the potential for worker fatigue to impact safety, especially during abnormal operations.
- New computer controls must be properly calibrated and tested for functionality before being used in any plant start-up process.
- Critical safety devices must not be bypassed during troubleshooting operations while in plant start-up or shut-down mode.
In summary, facility operators need to know exactly what equipment they have in any process that is being shut down or re-started; this is not always easy, especially in older plant where equipment may well have been changed in the past without a full record of the work. Much of the crucial information will be in the heads of older and more experienced personnel – assuming they have not yet retired (or been retired).
Greater use of sensors on equipment and the ongoing move towards full digitisation should help provide facility operators with a clearer idea of the equipment in their process units and also make it much easier to monitor performance during abnormal activities.
What will not change is the importance of effective MOC procedures. As CSB has highlighted before, a good MOC system involves input from a wide range of personnel and relies of good communication between all parties if it is to be effective.
The CSB Safety Digest can be downloaded from the CSB website.
[post_title] => Incidents: Not in vain
[post_status] => publish
[comment_status] => open
[ping_status] => open
[post_name] => incidents-not-vain
[post_modified] => 2018-07-24 12:30:05
[post_modified_gmt] => 2018-07-24 11:30:05
[post_parent] => 0
[guid] => https://www.hcblive.com/?p=9879
[menu_order] => 0
[post_type] => post
[comment_count] => 0
[filter] => raw
Abnormal plant operations, such as start-ups and shut-downs, present specific and unexpected hazards. Learning from recent incidents can help